Various contemporary surgical procedures require aspiration of fluids that may contain solid or semi-solid tissue or other debris. In many cases, the fluids may need to be aspirated from a body cavity such as from within the lens capsule of the eye or a cavity in a joint such as the shoulder or the knee. It is typically desirable to maintain an ambient or a super-ambient pressure within the body cavity during such surgical procedures. For example, the lens of a human eye may develop a cataractous condition that affects a patient's vision. Cataractous lenses are sometimes removed and replaced in a procedure commonly referred to as phacoemulsification. Phacoemulsification procedures are typically performed with an ultrasonically driven surgical probe that is used to break the lens within the lens capsule of the eye. The broken lens is removed through an aspiration line that is coupled to the handpiece and protrudes into the lens capsule. The handpiece has a probe with a tip that is inserted through an incision in the cornea. The handpiece typically contains a number of ultrasonic transducers that convert electrical power into a mechanical oscillating movement of the tip. The distal end of the tip has an opening that is in fluid communication with the aspiration line. The distal end of the tip can also have a sleeve that has an opening in fluid communication with an irrigation line. The irrigation line is typically connected to a pressurized source of fluid that can provide irrigation fluid to the surgical site. The oscillating movement of the tip breaks the lens into small pieces. Lens fragments can also be aspirated without any use of ultrasonic power either using a conventional ultrasonic handpiece or a dedicated aspiration probe that can eventually incorporate an irrigation port, better known as an irrigation/aspiration and the same concerns exist about flow control and vacuum surges described later. The lens pieces and irrigation fluid are drawn into the aspiration line through as aspiration opening on the tip. Phacoemulsification is more likely to be successful if super-ambient pressure can be maintained within the lens capsule and the anterior chamber of the eye during the procedure. However, fluid surges can be created after the distal end of the aspiration line is cleared from momentary obstructions by solid or semi-solid tissue. These fluid surges, also known as post-occlusion surges, can lead to transient aspiration flow rates through opening of the distal end of the surgical probe can transitorily exceed the flow rate through the irrigation line thereby causing eye chamber instability and an eventual collapse of the surrounding tissue. This instability can compromise the safety of the procedure of the eye, with potential undesirable damage to the posterior aspect of the lens capsule of the eye, and/or endothelium cells to be undesirably drawn away from the cornea and towards the distal end the tip of the handpiece. On the other hand, too high an irrigation flow rate may undesirably move endothelium cells away from the cornea, or undesirably cause endothelium cells to be aspirated out of the eye. Conventional phacoemulsification procedures are typically performed using a vacuum pressure of about 350 mmHg. There is a desire to increase the vacuum pressure to assist in aspirating lens fragments faster and with less auxiliary energy such as ultrasound. Lowering the ultrasonic work would be desirable because ultrasound can irritate the eye. Moreover, recent introduction of femtosecond laser assisted cataract surgery (FLACS) allows a laser induced significant softening of the lens material in many cataract procedures, making the use of ultrasonic energy unnecessary, only relying in aspiration of the laser-softened lens tissue material. Consequently, there is a desire to apply vacuums above 500 mmHg to improve the efficacy of aspiration thus reducing the amount of ultrasound delivered inside the eye, or the ability to safely and efficiently aspirate ultrasonically emulsified, laser-softened lens material or primitively soft lens material. However, such higher vacuum exacerbate the surgical risks associated with post-occlusion fluid surges into the surgical probe. Also for example, some orthopedic medical procedures produce particles or other debris that must be removed from a cavity within a joint such as in the shoulder or knee. To remove such particles the surgeon may couple an aspiration tube to the surgical site. The aspiration tube, which pulls the debris from the body, is typically connected to a canister, which is connected to a suction tube connected to wall suction. To ensure that the surgical site is properly distended during surgery, relatively large quantities of irrigation fluid are typically introduced to the body to continuously irrigate the surgical site, and an infusion pump is typically required to offset the high flow created by the hospital vacuum line. The introduction of such amounts of irrigation fluid into the body can cause undesirable or excessive extravasation of irrigation fluid into the surrounding tissue. Also, post-occlusion surges can be created when the suction line is obstructed by solid or semi-solid tissue. Such post-occlusion surges can lead to transient aspiration flow rates through the hospital vacuum line that substantially exceed the flow rate of irrigation fluid and thereby cause a sub-ambient pressure to be momentarily applied to the surrounding tissue. The momentary sub-ambient pressure condition may cause partial collapse of the body cavity, damage to tissue near the distal end of the aspiration tube, and/or undesired tissue or fluid to be drawn towards the distal end of the aspiration tube. Surgical aspiration systems may be designed to allow the surgeon to temporarily reverse the direction of aspiration flow by depressing a reflux switch or bulb attached to the system. The surgeon may do this, for example, if tissue is drawn towards the distal tip of the aspiration tube or handpiece that the surgeon does not desired to be drawn (e.g. tissue that the surgeon does not want to be damaged by the distal tip). The surgeon may also initiate reflux to clear or dislodge an occlusion at the distal tip of the aspiration tube or handpiece. Contemporary post-occlusion surge limiters can limit the vacuum surges within the aspiration system, but only when the vacuum created by the vacuum pump is limited to a level that is safe in consideration of the diameter and length of that surge limiter. For example, considering the typical dimensions of needles and tubing used in ophthalmology, the flow that would be generated by a 500 mmHg vacuum is above 250 cc/min which can undesirably collapse the eye. Therefore, prior art systems that use a Venturi pump must operate modest vacuum levels, e.g. below 300 mmHg unless very small needle bores are used. Such modest vacuum levels significantly limit the available un-occluded flow in such systems. Therefore, such surge limiters are typically not used with peristaltic pumps that will significantly increase the pressure difference in response to an occlusion of the aspiration tip. The absence of pressure rise in response to occlusion in the contemporary aspiration systems limits their ability to aspirate large tissue particles. Also, an in-line surge limiter may reduce the maximum flow rate in the absence of occlusion, even when the surgeon would prefer a higher flow rate to draw certain tissue towards the distal end of the tip (rather than moving the distal end of the tip towards the tissue). Also, an in-line surge limiter can undesirably reduce the maximum reflux flow rate.
Therefore, it would be desirable to provide an aspiration line flow regulator system that maintains a stable ambient or super-ambient pressure within a body cavity during a surgical procedure by limiting vacuum surges in the system.
For example, it would be desirable to provide an aspiration line flow regulator system that is configured such that the flow rate out of the body cavity through the aspiration line does not greatly, or for a prolonged period, exceed the flow rate into the body cavity. In cataract surgery, for example, aspiration flow should be sufficient to quickly engage and aspirate lens particles from the eye, however in the event of an occlusion the high vacuum created in the aspiration line may temporarily produce too high a flow after the occlusion break which could collapse the eye and produce damage.
It would also be desirable to provide an aspiration line flow regulator system that functions safely with limited or reduced flow rate of irrigation fluid through the irrigation line even when using the highest vacuum levels available.
It would also be desirable to provide an aspiration line flow regulator system that can safely take advantage of an aspiration pump that can significantly increase the relative vacuum response to an occlusion.
It would also be desirable to provide an aspiration line flow regulator system that would allow a high aspiration flow rate in the absence of an occlusion, and a reflux feature when commanded by the operator.
It would also be desirable to provide an aspiration line flow regulator system that could allow the use with advantage of the maximum vacuum levels achievable with improved safety and efficacy.
It would also be desired to provide an aspiration line flow regulator system that allows an operator to accurately control the flow rate from a surgical site while maintaining high vacuum levels to, for example, slowly but powerfully aspirate tissue fragments, reducing the need of use of complementary tissue disrupting energies such as ultrasonic emulsification.